The specific aims of this ongoing study are (1) to determine the efficacy of high fat diets containing various levels of Menhaden fish oil and corn oil on azoxymethane (AOM)-induced colon carcinogenesis in male F344 rats, and (2) to study the effects of caloric restriction and energy expenditure on AOM-induced colon carcinogenesis. In order to study the effect of high dietary fish oil on the initiating stage of colon carcinogenesis, groups of male F344 rats (35 days old) will be fed a low or high fish oil diet and at 56 days all animals will receive two weekly doses of AOM (15 mg/kg bw/wk). Two days later, groups of animals on high fish oil diet will be transferred to a low fish oil diet, whereas animals on low fish oil diet will be continued on the same diet. All animals will be necropsied at 36 weeks and colon tumor incidence compared. In order to study the effect of various levels of dietary fish and corn oil on post-initiating phase, groups of animals will be fed a low-fat diet and 2 days after AOM treatment (15 mg AOM, once weekly for 2 weeks) groups of animals will be transferred to high- fat diets containing various levels of fish oil and corn oil and continued on these diets until termination of experiment at 36 weeks. All animals will be necropsied and colon tumor incidences compared between various dietary treatments. With regard to the effects of caloric restriction and energy expenditure, 35 day old male F344 rats will be fed a high fat diet ad libitum and at 56 days of age, animals will be treated with AOM as described above. Two days later, groups of animals will be transferred to calorie- restricted diets or exercise cages but fed high fat diet ad libitum until termination of experiment at 36 weeks. Colon tumor incidence will be compared among the groups fed ad libitum and calorie-restricted diets and those subjected to exercise.